Neurology Center - A-Z Index

Spinal muscular atrophy

Spinal muscular atrophy is a group of disorders of the motor neurons (motor cells). These disorders are inherited and can appear at any stage of life. The disorder leads to muscle weakness and atrophy.

Alternative Names

Werdnig-Hoffmann disease; Kugelberg Welander

Causes

Spinal muscular atrophy (SMA) is a collection of different muscle diseases. Grouped together, it is the second leading cause of hereditary neuromuscular disease, after Duchenne muscular dystrophy
.

Most of the time, a person must get the defective gene from both parents to be affected. About 4 out of every 100,000 people have the condition.

The most severe form is SMA type I, also called Werdnig-Hoffman disease. Infants with SMA type II have less severe symptoms during early infancy, but they become weaker with time. SMA type III is the least severe form of the disease.

Rarely, SMA may begin in adulthood. This is usually a milder form of the disease.

A family history of spinal muscular atrophy is a risk factor for all types of the disorder.

Symptoms

Infants with SMA type I are born with very little muscle tone, weak muscles, and feeding and breathing problems.

With SMA type II, symptoms may not appear until age 6 months to 2 years.

Type III SMA is a milder disease that starts in childhood or adolescence and slowly gets worse.

Type IV is even milder, with weakness starting in adulthood.

Often, weakness
is first felt in the shoulder and leg muscles. Weakness gets worse over time and eventually becomes severe.

Symptoms in an infant:

Breathing difficulty, leading to a lack of oxygen

Feeding difficulty (food may go into the windpipe instead of the stomach)

Floppy infant (poor muscle tone)

Lack of head control

Little movement

Weakness that gets worse

Symptoms in a child:

Frequent, increasingly severe respiratory infections

Nasal speech

Posture that gets worse

Exams and Tests

The health care provider will take a careful history and perform a brain/nervous system (neurologic) examination to find out if there is:

Treatment

There is no treatment for the weakness caused by the disease. Supportive care is important. Attention must be paid to the respiratory system because affected people have trouble protecting themselves from choking. Breathing complications are common. Breathing can be assisted with invasive or noninvasive devices.

Physical therapy is important to prevent contractions of muscles and tendons and abnormal curvature of the spine (scoliosis
). Bracing may be needed. Surgery may be needed to correct skeletal deformities, such as scoliosis.

Outlook (Prognosis)

People with SMA type I rarely live longer than 2 - 3 years because of respiratory problems and infections. Survival time with type II is longer, but the disease kills most of those who are affected while they are still children.

Children with type III disease may survive into early adulthood. However, people with all forms of the disease have weakness and debility that gets worse over time. Adults who develop SMA often have a normal life expectancy.

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